There have been numerous attempts to develop a spinal implant to replace a damaged or degenerated natural spinal disc and to maintain sufficient stability of the disc space between adjacent vertebrae, at least until arthrodesis is achieved. These types of spinal implants have taken many forms.
For example, spinal implants can either be solid, sometimes referred to as a spacer or plug, or can define a hollow interior designed to permit bone in-growth, sometimes referred to as a fusion device or fusion cage. The interior of a fusion device may be filled with a bone growth inducing substance to facilitate or promote bone growth into and through the device. It is commonly accepted that spinal implants that facilitate or promote natural bone in-growth typically achieve a more rapid and stable arthrodesis. Some spinal implant designs are inserted into the disc space via a threading technique, while other designs are inserted into the disc space via a push-in or impaction technique.
One area that is usually not addressed by the above-discussed spinal implant designs concerns maintaining and restoring the natural anatomy of the fused spinal segment. Notably, once natural disc material is removed, the normal lordotic or kyphotic curvature of the spine is reduced or eliminated. With regard to prior spinal implants having a substantially uniform height, the need to restore this curvature is largely neglected. Additionally, in some cases, the adjacent vertebral bodies are reamed to form a passage having a shape corresponding to the particular shape of the spinal implant. In other cases, the normal curvature is established prior to reaming followed by insertion of the spinal implant. However, these techniques generally involve over-reaming of the posterior portion of the adjacent vertebral bodies, thereby resulting in excessive removal of load bearing vertebral bone which may lead to instability of the portion of the spinal column being treated. Also, it is typically difficult to ream through the posterior portion of the lower lumbar segment where lordosis is the greatest. As a result, limited effort or in some cases no effort has been made to restore the lordotic curvature. Consequently, a spinal curvature deformity may form as the vertebral bodies settle around the spinal implant.
Thus, there is a general need in the industry to provide an improved spinal implant and associated instrumentation. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.